Water Overlay

What are the Water Overlays

With the Water Overlays the following overlays are meant:

• Rainfall Overlay
• Flooding Overlay
• Groundwater Overlay

Each of these overlays have some common configuration steps which will be described on this page.

Tips on creating a new project when working with the Water Overlays

When creating a new project in the new project wizard, take into account the Advanced options. In this menu for example the AHN3 dataset can be selected, which, if available for your project area provides the most recent heightdata available as Open Data. Also, the IMWA dataset is already checked, this means that if available in your project area, Water Level areas and/or Culverts are already imported.

Configuration Wizard

Each of the Water Overlays has a configuration wizard which helps the user with configuring the overlay. The Configuration Wizard can be found in the General tab of the overlay.

For the Flooding Overlay the wizard has an extra step, the Rainfall and Groundwater Overlay wizard are basically the same. The settings in the wizard can always be changed after finishing the wizard by opening the wizard again and changing a value and recalculating the overlay.
Step 1 In the first step the simulation time is set, based on either a rainfall or without a rainfall. Also the evaporation reference factor (over time) can be set.

Step 2 In the second step the elements of the water system can be imported. In some sub-steps the there are four options: to do nothing and proceed, to import the data with the [[Geo_Data_Wizard|Geo data wizard], or when you already have the data imported to select it based on an attribute of the data or to let the Tygron Platform automatically generate some data. The following elements can be imported:

• the breach areas (only for the Flooding overlay
• water level areas; when automatically generating data one water level area covering the whole project area is created. The water level can be adjusted afterwards.
• ground water data
• sewer areas; can also be automatically generated based on the urbanization of the project area
• inundated areas; these are areas that are already inundated at the start of the flooding
• constructions

For the constructions keep in mind that when the data is point data, it has to overlap two water level areas. Therefore make sure the point data is on the border of two water level areas.

• • Weirs
  • Culverts
  • Pumps
  • Sewer overflows; if chosen to generate automatically the sewer areas, the sewer overflows can also be automatically generated

Step 3 Adjust, if needed, the hydrological coefficents used for the calculations for the surface terrain, the underground terrain and the function values (for example the amount of water storage for a certain type of building).
Step 4 The water system can be made visable with panels and a network visualization.
Step 5 In step 5 you have to choose the result types (the different results which can be exported) you want to see after the calculation is done. Some overlays require a threshold value. Read below for the different result types to choose from and the threshold values. One of the overlays can be selected as the first overlay, which then will be visible as the parent Overlay. You can always later adjust the result types you want to see and calculate the Overlay again. Also you can set the number of timeframes in the slider. The timeframes are the intermediate results of the calculation and are not the same as the timesteps. Each timeframe contains numerous timesteps, based on the grid cell size and the speed of the flooding (see for more information the Courant number). The more timeframes you choose, the more insight you will get into the calculation. Each of the timeframe results can be exported.
Step 6 In the last step, some additional result types can be chosen to be visualized. Thes overlays contain input data that is used for the calculation, for example the manning value.

Result types

Each Water Overlay is a grid overlay showing results on the surface (flooding), sub-surface (groundwater), open water and sewer system. The following results are produced:

Result type	Unit	Description
BASE_TYPES	nominal value	Division of gridcells in water, land, water level areas, sewer areas that are connected to the sewer, breach areas and hydrological constructions
CHLORIDE
DIRECTION	Degrees	The direction of the flooding
EVAPORATED	m (mm)¹	The amount of water that is evaporated
GPU OVERVIEW
IMPACTED_BUILDINGS	nominal value	Constructions impacted by flood: the value from the function value indicator is assigned to a building if the water depth at a grid-cell surrounding the building exceeds the overlay attribute value IMPACT_FLOOD_TRESHOLD_M
LAST SPEED	m/s	The speed of the flooding at the last calculated timestep
MAX SPEED	m/s	The maximum speed of the flooding of all the calculated timesteps
NITROGEN
PHOSPHORUS
SEWER_LAST_VALUE	m (mm)¹	The amount of water in the sewer storage at the last calculated timestep
SEWER_MAX_VALUE	m (mm)¹	The maximum amount of water in the sewer storage of all the calculated timesteps
SURFACE_DURATION	s (min)¹	The amount of time the water depth in a cell exceeds the value set in the overlay attribute value SHOW_DURATION_FLOOD_LEVEL_M
SURFACE_FLOW	m3/m2	Total volume of water passed a grid-cell, scaled by the cell surface (grid cell-size^2)
SURFACE_LAST_VALUE	m (mm)¹	The water depth at the last calculated timestep
SURFACE_MAX_VALUE	m (mm)¹	The maximum water depth of all the calculated timesteps
UNDERGROUND_FLOW	m³/m²	Total infiltration amount from the surface to groundwater
UNDERGROUND_LAST_STORAGE
UNDERGROUND_LAST_VALUE	m (mm)¹	The amount by which the groundwater table has risen above the initial groundwater level at the last calculated timestep
UNDERGROUND_MAX_STORAGE
UNDERGROUND_MAX_VALUE	m (mm)¹	The maximum amount by which the groundwater table has risen above the initial groundwater of all the calculated timesteps
UNDERGROUND WATERTABLE
WATER_STRESS	m (mm)¹	The maximum water depth during the simulation (almost the same as the SURFACE_MAX_VALUE, but at the terrain type water only a water depth is shown if the depth exceeds the overlay attribute value ALLOWED_WATER_INCREASE_M)

¹ the units between () are as displayed in the 3D client. If exported to GTiff the SI-convention is used: meters (m) and seconds (s).

General Tab

The General Tab can be found at the panel on the right side, when selecting a Water Overlay. In this tab several settings can be adjusted.

Calculation Preference

Here you can manipulate the computation time step by choosing between the option SPEED, AVERAGE and ACCURACY. The computational timesteps will be set according to the Courant criterion:

Δt = Δx /u_max

where:

• Δt = computational timestep
• Δx = grid cell size
• u_max = max velocity, assumed 2.5 (SPEED), 5 (AVERAGE) and 10 (ACCURACY) m3/s respectively

Grid cell size

The Tygron Platform computes flow equations over a rectangular cartesian grid, the grid cell size can be set by clicking on Change Grid. After the grid cell size is changed, the Overlay is immediately being recalculated. Note: if you choose a smaller grid cell size, both the amount of time steps (see Calculation Preference) and amount of computational cells increase.

Refresh Grid

By Refreshing the grid, the Overlay is recalculated. This may take some time, depending on the grid cell size, the size of your project and the calcualtion preference. Below some use cases when to use Refresh Grid:

• when you have changed a setting in the Configuration Wizard, but not clicked on the Finish button of the wizard.
• when you change the Result type or calculcation preference in the General tab
• when you change the legend in the Legend tab
• when you change the keys in the Keys tab
• when you change the attrbutes of the Overlay in the Attributes tab

Export Grid File

You can export the current result type as either a GeoTiff (binary file/bitmap image can be opened in a GIS or in an image viewer) or ASCII (text file, can also be opened in a GIS but is also readable in a text editor) file. Also, it is possible to export the difference result type of the current and maquette situation.

Save Overlay result

With this option you can create a duplicate inactive copy of the current overlay. This is noticeable in the Overlays panel on the left side of the screen. The duplicated overlay will have (inactive copy) behind the overlay name and is greyed out. This copy is not being recalculated when changing settings in the original duplicated overlay. When checking the checkbox: active in simulation, the copy becomes active again and can be recalculated. Also the overlay name is again in black and not grayed out anymore.

Show Water Balance

The Water Balance panel shows the in- and outflow of water in m3. The Water Balance panel is also visible when clicking on the Debug info (see below). The water balance is made up of the following components (dependent on what is in the project):

• Land surface: amount of water on the land surface after simulation (m3)
• Water surface: amount of water stored on water cells after simulation (m3)
• Building storage: amount of water stored in building storage (m3)
• Sewer storage: amount of water stored in sewers after simulation (m3)
• Underground storage: amount of water stored in the sub-soil after simulation (m3)
• Evaporated: amount of water evaporated after simulation (m3)
• Outlet: amount of water extracted from the model during the simulation via outlets of water areas or sewer pumps (m3).

Warnings

When the grid cell size is too large in combination with the project size, a warning pops up. This means that calculated results are not accurate. The solution to this is to change the grid cell size to a smaller number.

Debug Info

The debug info contains the following information:

• Rain: the amount of rainfall (mm) in the duration of the rainfall event (hours)
• Total Simulation: the simulation period (hours)
• Cells: The dimensions of the simulation: the amount of computational cells and the amount of time steps (cycles)
• Water areas:
• Weir flow: the amount of water flown over weirs during simulation (m3)
• Sewer overflow: the amount of water flown over sewer overflows during simulation (m3)
• GPU time: the computation time on GPU (seconds)
• Volume: total volume of the in- and outflow of water in the model.

If you click on the Debug Infom the Water Balance panel pops up.

Keys tab

The tab Keys refers to the settings for the water system (areas and constructions) that are adjusted by following the configuration wizard in the General tab. It is therefore generally not needed to change the keys in this tab, as this can be done also in the configuration wizard. However, below an explanation of the Keys for areas and buildings.

Attribute	Unit	Description
Water Level	m + datum	initial water level, relative to datum, for all water cells in a water area
Outlet	m3/s	water abstraction for all water cells in a water area
Outlet level	m + datum	initial water level, relative to datum, for all water cells in an outlet area (breach for example)
Outlet capacity	m3	maximum amount of water that can be used for the outlet
Sewer Storage	m	available storage in sewers at the start of simulation in a sewer area
Sewer Pump Speed	m3/s	sewer water abstraction for all cells in a sewer area

Keys referring to constructions (building attributes)

Attribute	Unit	Description
Weir Height	m + datum	weir crest level
Weir Output	m3/s	The amount of water that flows through a weir/culvert
Weir Coefficient		linear weir coefficient for accounting discharge & contraction losses
Culvert Speed	m3/s	the discharge capacity of a culvert
Pump Speed	m3/s	the capacity of a pump
Sewer Overflow Height	m + datum	the height of a crest of a sewer overflow
Sewer Overflow Speed	m3/s	the discharge capacity of a sewer overflow
Chloride	mg/m2
Nitrogen	mg/m2
Phosphorus	mg/m2

Attributes tab

This tab shows the attributes of result types that can be adjusted. These attributes can also be adjusted in the configuration wizard in step 5 in the General tab. It is therefore generally not needed to change the attributes here. However, below an overview of the Overlay Attributes.

Attribute	Unit	Description
ALLOWED_WATER_INCREASE_M	m	increment by which the water level on a water cell is allowed to increase before the depth is shown in the WATER_STRESS result type
AVG_SURFACE_WATER
DESGIN_FLOOD_ELEVATION_M	m
GROUND_BOTTOM_DISTANCE_M	m
GROUND_WATER
IMPACT_FLOOD_THRESHOLD_M	m	maximum waterdepth around a building where after the building is assumed impacted shown in the IMPACTED_BUILDINGS result type
MAX_SPEED_MS
MIN_SLOPE		slope whereunder the pressure slope is assumed 0
SEWER_OVERFLOW_THRESHOLD		fraction of storage whereafter sewer overflows take place
SHOW_DURATION_FLOOD_LEVEL_M	m	threshold value of the amount of water on a grid cell that is used for the SURFACE_DURATION result type
SUPERGRID
SURFACE_WATER_EVAPORATION_FACTOR
TIMEFRAMES		the number of intermediate (overlay) results you would like to see of the calculation. A timeframe is not the same as a timestep. A timeframe is an intermediate (overlay) result and can contain already a number of timesteps. The number of timesteps is based on the grid cell size and the speed of the flooding (see for more information the Courant number).